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Light stopped for a minute

Photonics SpectraOct 2013
DARMSTADT, Germany – At 186,000 miles per second, the speed of light is unparalleled, so slowing it down is a formidable challenge – and stopping it seems impossible. But physicists in Germany report using a glasslike crystal to stop light for about one minute, which could have important implications for light-based data processing.

Thomas Halfmann and colleagues at the Institute of Applied Physics at the Technical University Darmstadt achieved the record by combining various known methods. In addition to stopping light, they also stored images transferred by the light pulse into a crystal for the duration of a minute – a million times longer than previously possible.

Researchers at the Technical University of Darmstadt used a glasslike crystal containing a low concentration of praseodymium ions in a setup that also included two laser beams to stop light for a minute. Photo courtesy of Katrin Binner
Over the past decade, researchers have reported short stop times for simple light pulses in extremely cold gases using special crystals. The Darmstadt researchers used a glasslike crystal containing a low concentration of praseodymium ions in a setup that also included two laser beams.

The first (control) beam changes the optical properties of the crystal so that when the second beam comes into contact with the crystal and the first light beam, it decelerates. When the physicists switched off the first beam precisely when the second beam was within the crystal, the decelerated beam came to a stop.

The team was able to store a simple image of three striped lines within the crystal. The information was read out by turning the control laser beam on again.

Professor Thomas Halfmann and colleagues have stopped light by combining known optics-related methods. Photo courtesy of Katrin Binner
How well the system works depends strongly on the parameters of the driving optical fields, magnetic fields and the high-frequency pulses, the researchers said. Computer algorithms optimized these factors so that the spin waves formed by freezing the beam could
survive inside the crystal for as long as possible.

They now intend to explore techniques that can store light significantly longer – perhaps for a week – and to achieve a higher bandwidth and data transfer rate for efficient information storage via stopped light.

A solid with a structure that exhibits a basically symmetrical and geometrical arrangement. A crystal may already possess this structure, or it may acquire it through mechanical means. More than 50 chemical substances are important to the optical industry in crystal form. Large single crystals often are used because of their transparency in different spectral regions. However, as some single crystals are very brittle and liable to split under strain, attempts have been made to grind them very...